By Dietzel M.
Expanding attempt of the medical neighborhood is dedicated to downsize technical devices regarding fluids to levels among sub-millimeter and nano-meter scales. this isn't in simple terms a result of curiosity in process miniaturization but additionally to novel operating rules hidden within the dominance of surface-related actual phenomena that are negligible in greater, volume-controlled structures. Microfluidic platforms inherit, subsequent to their technical possibilities, basic clinical demanding situations because they include either, phenomena which derive from continuum results and phenomena that are obtainable via a molecular view element merely. This has definite implications om the modeling of those structures: types completely in response to the continuum technique fail to foretell the procedure habit, while versions engaged on the molecular scale are hugely inefficient. Hybrid modeling ways are as a result required, frequently in type of adjustments and extensions of the continuum technique. during this context, the importance of thermocapillary convection brought about in axisymmetric micro-flows of technical relevance is investigated herein. An in-house cutting-edge Finite aspect solver of the Navier-Stokes equations and effort equation in Lagrangian coordinates is prolonged to include a temperature-dependent floor stress and to safely version the movement of the touch line (i.e. wetting). The already embedded solidification version is supplemented for evaporative section swap. The version is utilized to the deposition and solidification of micron-sized solder droplets utilized in the flip-chip undefined, to the thermocapillarity-induced rupture of capillary bridges in addition to to the quasi-isothermal printing and laser-induced heating of colloidal nanoparticle suspension beverages ('nanoinks'). The microfluidic version is prolonged within the latter case to trace the inertia-controlled movement of suspended debris subsequent to a monodispersed particle coagulation version. The numerical simulations are in comparison the place attainable with experiments. it truly is verified that Marangoni convection via an asymmetric evaporation at ambient stipulations is negligible, while all non-quasi-isothermal investigations express a non-negligible impression of the thermocapillary strength. It provides in case of the solder drop deposition to the hassle in lowering the footprint dimension via thermocapillarity-driven dewetting results. within the opposite, it factors within the nanoink software an undesired displacement of the ink from the heart zone radially outwards, inflicting a attribute bowl form of the particle constitution shaped. The inertia-controlled particle version finds particle structuring results in area of the substrate while the coagulation version indicates utilizing a laser mild absorption intensity within the order of the droplet top to make sure a uniformly agglomerated particle constitution. The latter is of specific significance for electrically carrying out constructions. The learn on particle coagulation in nanoinks is supplemented by means of a vapor bubble version round a unmarried nanoparticle heated via laser gentle absorption. This version is meant to come to a decision even if particle coagulation proceeds basically within the gasoline or the liquid section. numerous technical and numerical concerns have been resolved subsequent to the medical perception in the course of the improvement of this thesis. between these, the implementation of a public area meshing regimen within the fluid solver rather than the formerly applied advertisement meshing application is the main large one. It improves the portability of this system with admire to assorted computational structures in addition to the neighborhood mesh answer and the computational time. the current research demonstrates in an unique model the technical versatility of thermocapillary circulate in microfluidic platforms. It issues out new actual points, particularly within the interplay of Marangoni stream with wetting/de-wetting results. It highlights the main promising extensions of the continuum version to account for Gibbs loose power pushed spreading on the touch line. furthermore, it describes the monitoring of discrete debris suspended in liquid domain names with arbitrarily relocating limitations. regardless of the technical relevance of particle suspension beverages with a unfastened floor, the current thesis is without doubt one of the first modeling makes an attempt of this sort of difficulties. A monodispersed particle coagulation version on hand from the literature and basically derived for aerosols is changed to the current challenge and mixed in a special style with the unfastened floor microfluidic version, supplying a profound and effective instrument for destiny stories.
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Additional resources for Modeling of the Surface Deposition and Thermal Treatment of Plain Liquids, Melts And Nanoparticle Inks Multiscaled/Multiphase Phenomena and Engineering Applications
The Marangoni effect was shown to assist in novel small-scale applications due to its finedosed force value, [20, 21], as more extensively discussed in chapter 4. Here, we want to generally concentrate on a temperature-dependent surface tension only. 50) applies for the bulk liquid pressure. 51) −a Although the tangential pressure in the interfacial region itself is dominated by the negative cohesive pressure, the change of the tangential pressure is dictated by the strongly varying kinetic pressure.
The concept of line tension corrects for this approximation , which might be important for high-energy substrates with long-range intermolecular interaction. However, the correction is usually small and is therefore neglected here. The situation becomes more complicated if the contact line is allowed to move. e. no material stream crosses the free surface and the free surface line is a streamline. In case that the classical no-slip and no penetration condition are enforced at the wall, this streamline leads to a stagnation point, which is located on the contact line.
The fundamental difference between a free surface and the bulk of a liquid is the reduced intermolecular binding energy of the molecules at the free surface . The unbalanced intermolecular forces lead by experience to a minimization of the surface area to attain equilibrium. 2 a), although it contains two serious shortcomings: it neither represents a 20 state of mechanical equilibrium at the interface nor it explains a surface tension parallel to the interface, since the resulting force is directed inwards with respect to the interface .